A new cobalt triangular prism supramolecular flask: Encapsulation of a quinhydrone cofactor for hydrogenation of nitroarenes with high selectivity and efficiency

Article abstract of DOI:10.1016/j.inoche.2019.107558

A new M₆L₃ metal-organic triangular prism host Co–L¹ was synthesized that contains a sufficiently large cavity for encapsulation of a quinhydrone (QHQ) electron transporter to form charge-transfer complexes for accelerating electron delivery. Through the strong coordinating ability of the ONP chelator, a suitable redox potential was obtained for the combination of light-driven proton reduction with the selective hydrogenation of nitro groups. The experimental results showed that the regulation of redox potential is very beneficial for hydrogen production and that the introduction of QHQ accelerates electron transfer and increases the reaction rate. Control experiments based on an inhibitor and a mononuclear compound resembling the cobalt corner of the triangular prism suggest enzyme-like behaviour. This synthetic platform, in which the supramolecular systems exhibit high activity and stability, provides an alternative strategy to selectively hydrogenate nitroarenes using light as a clean energy source.

Full text of DOI:10.1016/j.inoche.2019.107558

InorganicChemistryCommunications109(2019)107558
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
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Short communication
A new cobalt triangular prism supramolecular flask: Encapsulation of a
quinhydrone cofactor for hydrogenation of nitroarenes with high selectivity
and efficiency
Sijia Zheng, Liang Zhao⁎, Jianwei Wei, Cheng He, Guangzhou Liu, Chunying Duan
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, PR China
G R A P H I C A L A B S T R A C T
A metal-organic prism with suitable redox potential was constructed for the encapsulation of a quinhydrone cofactor to selectively reduce nitroarenes.
A B S T R A C T
A new M6L3 metal-organic triangular prism host Co–L1 was synthesized that contains a sufficiently large cavity for encapsulation of a quinhydrone (QHQ) electron
transporter to form charge-transfer complexes for accelerating electron delivery. Through the strong coordinating ability of the ONP chelator, a suitable redox
potential was obtained for the combination of light-driven proton reduction with the selective hydrogenation of nitro groups. The experimental results showed that
the regulation of redox potential is very beneficial for hydrogen production and that the introduction of QHQ accelerates electron transfer and increases the reaction
rate. Control experiments based on an inhibitor and a mononuclear compound resembling the cobalt corner of the triangular prism suggest enzyme-like behaviour.
This synthetic platform, in which the supramolecular systems exhibit high activity and stability, provides an alternative strategy to selectively hydrogenate ni-
troarenes using light as a clean energy source.
1. Introduction
accessible nitroarenes, which presents a serious obstacle to realizing the
specific selective hydrogenation of nitro groups. Although various cat-
alysts have been designed and synthesized for achieving highly efficient
and selective hydrogenation of nitro groups [8,9], some of them still
face considerable difficulties and challenges in practical production,
including limited substrate scope, depletion of conventional energy and
the danger of handling high-pressure hydrogen gas as a hydrogen
source.
Functional aromatic amines are one of the most important inter-
mediates and are widely used in dyes, agrochemicals and pharmaceu-
tical synthesis [1,2]. They can be prepared by reductive amination [3],
reduction of nitriles [4,5] and direct amination of alcohols [6,7]. The
challenge for these methods is the selectivity of nitroarene reduction
due to the influence of the multiple unsaturated functional groups of
⁎ Corresponding author.
E-mail address: zhaol@dlut.edu.cn (L. Zhao).
https://doi.org/10.1016/j.inoche.2019.107558
Received 2 August 2019; Received in revised form 23 August 2019; Accepted 29 August 2019
Availableonline30August2019
1387-7003/©2019ElsevierB.V.Allrightsreserved.

S. Zheng, et al.
InorganicChemistryCommunications109(2019)107558
In recent years, simulating enzymes in nature and using clean en-
2. Results and discussion
ergy to realize chemical transformations under mild environmental
conditions have been widely researched [10–13]. To attain the high
efficiency and selectivity of enzymatic systems, chemists have used
metal-organic hosts with defined hydrophobic cavities to mimic the
remarkable properties of enzyme pockets for catalysing unique che-
mical transformations [14–19]. On the other hand, nature has devel-
oped untold millions of redox systems, in which redox processes are
catalysed by numerous species of enzymes in the presence of the cor-
responding cofactors [20–23]. Among these cofactors, as a coenzyme,
quinhydrone (QHQ) can effectively transfer electrons and protons
through redox cycling between its oxidation state and reduced state
[24].
Ligand H4L1 (5,5′-methylenebis(N1,N3-bis(2-(diphenylpho-sphanyl)
benzylidene)isophthalo hydrazide)) was obtained by Schiff base reac-
tion of 5,5′-methylenedi(isophthalohydrazide) with 2-(diphenylpho-
sphanyl)benzaldehyde in an ethanol solution and characterized by
elemental analysis and spectroscopic methods. The solution-phase sta-
bility of compound Co–L1 and the host-guest behaviour of binding QHQ
were characterized by electrospray ionization-mass spectrometry (ESI-
MS). Three intense, sharp peaks at m/z = 801.6560, 974.3839, and
1233.4789 (Fig. 2a) are assigned to [Co6(L1)3]6+, [Co6(L1)3·NO3
]
−
5+
and [Co6(L1)3·2NO3
]
4+, respectively, indicating the formation of the
−
M6L3 species in solution. Co–L1 was shielded by a total of forty-two
benzene rings to form a spherical cavity, providing a hydrophilic en-
vironment for the encapsulation of the bio-inspired QHQ cofactor in the
host. When five equiv. of QHQ was added into the acetonitrile solution
of Co–L1, a new intense, sharp peak at m/z = 1275.7515 was observed,
Recently, we constructed an artificial charge-transfer complex
system by encapsulating a QHQ cofactor for the photocatalytic gen-
eration of hydrogen in combination with the hydrogenation of ni-
trobenzene [25]. This previous study discussed that the formation of
host-guest systems and changes in the overpotential of the metal sites
influenced the efficiency of the light-driven hydrogen production and
the hydrogenation of nitrobenzene. The results indicated that the co-
balt-based metal-organic triangular prism with CH2 centres has pro-
minent advantages for the formation of host-guest systems and catalytic
performance. In this work, the intrinsic redox potential of the cobalt-
based metal-organic triangular prism, the electron transfer of QHQ
outside the cavity and the reduction selectivity of nitro compounds
were considered. By introducing four strong ONP chelators on the CH2-
centred ligand to replace the previously reported ONN chelators, we
assembled herein a new redox-active cobalt-based metal-organic tri-
angular prism host with a suitable redox potential, and the catalytic
performance was evaluated (Fig. 1). We envisioned that the introduc-
tion of coordinated phosphorus atoms would help shift the redox po-
tentials of the coordinated metal sites to more negative potentials, and
these donor atoms could be engineered into this new complex to ac-
celerate the photocatalytic hydrogen generation in combination with
the selective hydrogenation of nitrobenzene to anilines. The experi-
mental results indicated that the special redox-modulated environment
of the host and the proximity effects of the host-guest interaction could
promote the formation of the charge-transfer complex to decrease the
overpotential and that the cofactor QHQ could accelerate the electron
transfer outside the cavity to further improve the efficiency of selective
nitroarene hydrogenation.
which could reasonably be attributed to
a
[Co6(L1)3·(QHQ-
2H)·CH3CN·2H2O]4+ species. A comparison of the experimentally ob-
tained peak with that from the simulated natural isotopic abundances
conforms to the formation of a 1:1 stoichiometric host-guest complex
species Co–L1 ⊃ QHQ in solution (Fig. 2b).
The cyclic voltammogram of Co–L1 suggested that the reduction
processes of CoII/CoI and CoIII/CoII occurred at approximately −1.41
and −0.69 V (vs. Ag/AgCl), respectively (Fig. 3a). Compared with the
previously reported ONN chelators, the CoII/CoI potential shifted 0.24 V
towards more negative potential, which indicated that the compound
Co–L1 has higher reduction activity for hydrogen production [26]. This
effect could be attributed to the introduction of “P” coordination sites in
the Co–L1 structure. The CoII/CoI potential falls well within the po-
tential range of proton reduction in aqueous media. After the addition
of p-toluenesulfonic acid (0.8 mM) to the Co–L1 solution, the voltam-
mogram showed the appearance of a new peak at −1.57 V. Moreover,
the intensity of the new wave increased with increasing concentrations
of p-toluenesulfonic acid (Fig. 3a) [27]. The new wave was reasonably
assigned to typical proton reduction, suggesting that Co–L1 is capable of
directly reducing protons in a catalytic reaction [28,29]. The appear-
ance of these redox peaks proves that Co–L1 can achieve proton re-
duction with high efficiency [30–32].
The Co–L1 was firstly investigated as a catalyst for light-driven
hydrogen production in a 20 mL flask. Under the optimized conditions,
Fig. 1. Procedure for the synthesis of the metal-organic triangular prism and schematic representation of using a supramolecular system for the encapsulation of a
quinhydrone cofactor within the cavity of the supramolecular triangular prism to combine light-driven proton reduction and selective hydrogenation of nitroarenes.
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S. Zheng, et al.
InorganicChemistryCommunications109(2019)107558
Fig. 2. ESI-MS spectra of (a) Co–L1 and (b) Co–L1 following the addition of 5 equiv. of QHQ in CH3CN. The insets show the measured and simulated isotopic patterns
at m/z = 801.6560, 974.3839, 990.7917 and 1275.7515.
Fig. 3. (a) Cyclic voltammograms of Co–L1 (0.1 mM) in CH3CN containing 0.1 M TBAPF6 (black line) and following the addition of p-toluenesulfonic acid. (b) Volume
of hydrogen produced by the systems containing different catalysts (red bars, Co–L1: 2.5 μM, Co–L2: 15.0 μM), Ru(bpy)3 (0.5 mM) and H2A (0.1 M) in a CH3CN/
2+
H2O solution (1:1, pH 4.75). The green and cyan bars show the hydrogen volumes generated by the systems containing QHQ (15 mM) and QHQ/DFB (15 mM/
0.15 M), respectively. (c) ITC experiments on Co–L1 upon the addition of QHQ or DFB showing the formation of host-guest complexes in CH3CN. (d) UV/Vis
absorption difference spectra of Co–L1 (0.2 mM) in CH3CN upon the addition of QHQ (0.3 mM). The insets show the linear plot of c/A against 1/A1/2 to estimate the
association constant (Ka). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
3

S. Zheng, et al.
InorganicChemistryCommunications109(2019)107558
hydrogen was directly generated under continuous irradiation with a
the Co–L2/QHQ system is postulated to result from the well-defined
host-guest interactions and the proximity effects created by the host
architecture.
2+
CH3CN/H2O (1:1, v/v) solution containing Ru(bpy)3
(0.5 mM),
Co–L1 (2.5 μM), and ascorbic acid (H2A, 0.1 M) at a pH of 4.75 with
light from a 500 W Xe lamp (Figs. S8–S10). The maximum volume of
hydrogen produced reached 0.29 mL after 12 h (Fig. 3b) and was three
times that of the previous similar system, except for the redox potential
of the catalyst [25], indicating that the ONP chelators could regulate
the potential of metal centres to facilitate proton reduction. Control
To further investigate the influence of the formation of host-guest
charge-transfer complexes in the photocatalytic hydrogen evolution
process, p-difluorobenzene (DFB), a redox-inactive species, was se-
lected as an inhibitor for our enzymatic system. ITC curves of Co–L1
after adding DFB revealed the formation of a host-guest system with an
association constant of 3.93 × 104 (Figs. 3c and S7). The higher binding
constant than that of the Co–L1/QHQ system indicates that DFB could
replace QHQ and be encapsulated in the pocket of the capsule. As ex-
pected, hydrogen production sustained only an increase of 10% in the
presence of QHQ (15 mM) and DFB (0.15 M) (Fig. 4b). However, when
DFB was added to the Co–L2/QHQ reaction system, there was no sig-
nificant influence on hydrogen production (Fig. 3b). The continual
catalysis of similar molecules is unique to enzyme systems, and the
results indicated that the catalytic effect of the system is inhibited due
to the presence of host-guest complexes.
2+
experiments demonstrated that host Co–L1, photosensitizer Ru(bpy)3
and electron donor H2A are three indispensable elements for hydrogen
generation. Of course, these proton reduction systems could not work
well without light.
Under the optimized conditions, the addition of QHQ (15 mM) to
the aforementioned reaction solution increased the hydrogen produc-
tion to 0.62 mL (Fig. 3b) with an approximately 2200 of turnover
number (TON), indicating that the formation of host-guest complex
promotes occurrence of the hydrogen production (Fig. S11). Isothermal
titration microcalorimetry (ITC) was used to ensure the quantitative
accuracy of the relationship between the compound Co–L1 and the
cofactor QHQ as well as provide insight into the thermodynamics for
host-guest complexation [33–35]. A typical titration curve is shown in
Fig. 3c with the observed inclusion number 1 between Co–L1 and QHQ.
Curve fitting by the computer simulation using an “independent” model
reveals an association constant of 2.92 × 104 M−1 with an activation
The introduction of the ONP chelators endows these metal-organic
supramolecular systems with an appropriate redox potential to allow
photocatalytic reduction of protons to form active H-atoms that can
selectively reduce reaction intermediates or substrates [37,38]. In a
typical model reaction, p-nitroacetophenone with bifunctional groups
was used as the substrate for the selective reduction of the nitro group.
enthalpy (ΔH) of 0.27 kJ·mol−1
,
activation entropy (ΔS) of
The addition of 40 mM p-nitroacetophenone to a solution containing
86.43 J·mol−1 and Gibbs free energy (ΔG) of −25.50 kJ·mol−1 for
Co–L1 ⊃ QHQ (Fig. S6). And the formation of host-guest charge-
transfer complex was further demonstrated by UV/Vis differential ab-
sorption spectra, with a new absorption peak at 590 nm (Fig. 3d) [36].
The titration data result in the association constant of 3.20 × 104 M−1
for a 1:1 complex, which is in good consistent with the results in the
ESI-MS and ITC spectra. Notably, Co–L1 and QHQ have no absorption
peak at this region, which suggests the formation of host-guest charge-
transfer complexes. The results of the ESI-MS spectra, ITC, and UV/Vis
spectra were mutually confirmed, indicating that a 1:1 mol ratio host-
guest Co–L1 ⊃ QHQ coclathration supramolecular system was formed
stably in solution. Moreover, the addition of QHQ (0.2 mM) to a solu-
tion containing Co–L1 (0.1 mM) resulted in a new irreversible peak at
approximately −1.56 V (Fig. S13). This modified potential shifted
0.15 V towards more negative potential compared to the intrinsic po-
tential (−1.41 V) of the compound Co–L1 and may be attributable to
the host-guest charge-transfer supramolecular system, which facilitates
proton reduction more easily.
Co–L1 (2.5 μM), H2A (0.1 M), and Ru(bpy)3
(0.5 mM) resulted in a
2+
33% yield, and the selectivity of the product p-aminoacetophenone
reached 99%. Under the same conditions, with the addition of QHQ
(15 mM) to the aforementioned reaction solution, a yield of 48% with a
turnover number (TON) of 7700 per mole of catalyst was obtained, and
the TOF was as high as 650 per mole of catalyst per hour. After 12 h of
irradiation, only a trace amount of p-nitrophenylmethanol was de-
tected, and the hydrogen evolution was stopped, which suggested that
this supramolecular system was highly efficient and stable. Interest-
ingly, when the concentration of Co–L1 was fixed at 2.5 μM, the TOF of
the photocatalytic reduction of p-nitroacetophenone increased with
increasing QHQ concentration, and the TON reached a maximum of
11,600 at 30 mM. However, the TOF as high as 970 per mole of catalyst
per hour remained unchanged when the QHQ concentration continued
to increase (50 mM) (Fig. 4c). We speculated that a high concentration
of substrate could inhibit the formation of the Co–L1 ⊃ QHQ host-guest
complexes to influence the reaction efficiency (Fig. S5).
To demonstrate the general applicability of our catalyst system,
various nitroarenes were tested (Table 1). The results showed that the
carbonyl group cannot be reduced due to the insufficient reduction
potential of both the photosensitizer and the host-guest complex. The
selectivity of all corresponding amino products reached 99% with high
Under saturated reaction conditions, QHQ in high concentration
(Kass[QHQ] > 100) exhibited pseudo-zero-order kinetics of hydrogen
production. The initial turnover frequency (TOF) of hydrogen produc-
tion was no longer increased by further adding QHQ. When the con-
centration of QHQ was fixed at 15 mM, the TOF exhibited a linear re-
lationship with the concentration of Co–L1 in the range of 1.0 μM to
2.5 μM (Fig. 4a). However, the increase of multiples in TOF was more
than that of the concentration of Co–L1. This result indicated that the
TOF depends on the concentration of complex Co–L1 ⊃ QHQ and that
excess QHQ could also accelerate the electron transfer to increase the
TOF of hydrogen evolution outside the cavity. To further explore this
type of system, the ligand HL2 (N′-(2-(diphenylphosphanyl)benzyli-
dene)benzohydrazide) was synthesized by benzhydrazide and 2-(di-
phenylphosphanyl)benzaldehyde and self-assembled with cobalt ions to
generate a mononuclear cobalt complex Co–L2 (Fig. S1). Then, control
experiments of light-driven hydrogen generation were performed with
Co–L2 containing the same coordination configuration under the same
conditions. The volumes of hydrogen generation were 0.23 and 0.27 mL
for Co–L2 instead of Co–L1 in the absence and presence of the QHQ
cofactor, respectively (Fig. 3b). An increase of 20% was observed,
which was attributed to the ability of the QHQ cofactor to facilitate
electron transfer in normal homogeneous systems. The superior hy-
drogen-evolving performance of the Co–L1/QHQ system over that of
TON values. For
a time-course experiment, an excess of p-ni-
troacetophenone (0.1 M) was added, and H2A was added into the re-
action system halfway through the experiment to ensure that the H2A
concentration remained at 0.1 M. After 60 h, the TON value reached
18,000. Most importantly, when QHQ (30 mM) was added to the
system, the TON value reached 36,000 through 6 superimposed ex-
periments (Fig. 4d).
3. Conclusions
In summary, a new strategy for the construction of a host-guest
charge-transfer system was further developed to accelerate photo-
catalytic hydrogen generation and the selective hydrogenation of ni-
troarenes. The approach included the self-assembly of the well-designed
redox-active metal-organic prism host, which has a suitable pocket size
and a special redox-modulated environment to encapsulate the QHQ
cofactor, benefitting the formation of a charge-transfer complex. The
enhanced electron transfer efficiency due to the proximity effects of the
host-guest systems, the well-localized redox events and the electron
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S. Zheng, et al.
InorganicChemistryCommunications109(2019)107558
2+
Fig. 4. (a) Light-driven hydrogen evolution of systems containing QHQ (15 mM), Ru(bpy)3
(0.5 mM), H2A (0.10 M) in a CH3CN/H2O solution (1:1, pH = 4.75)
with different concentrations of Co–L1. The insets show the linear plot of the hydrogen production rate against the concentration of Co–L1. (b) Light-driven hydrogen
evolution of the system containing Ru(bpy)3 (0.5 mM), H2A (0.1 M), and Co–L1 (2.5 μM) in CH3CN/H2O (1:1, pH 4.75, black line) and following the addition of
2+
15 mM QHQ (red line) or both 15 mM QHQ and 0.15 M DFB (blue line). (c) Light-driven selective nitro reduction of the system containing p-nitroacetophenone
(40 mM), Ru(bpy)32+ (0.5 mM), H2A (0.1 M), Co–L1 (2.5 μM) in CH3CN/H2O (1:1, pH = 4.75) with different concentrations of QHQ. The insets show the linear plot
of TOF against the concentration of Co–L1. (d) Light-driven selective nitro reduction of the system containing p-nitroacetophenone (0.1 M), Ru(bpy)3 (0.5 mM),
2+
H2A (0.1 M), and Co–L1 (2.5 μM) in CH3CN/H2O (1:1, pH = 4.75, black line) and following the addition of 30 mM QHQ (red line). (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of this article.)
Table 1
The selective reduction of nitroarenesa.
aReaction conditions: Substrate (40 mM), Co–L1 (2.5 μM), Ru(bpy)3
(0.5 mM), H2A (0.1 M), and QHQ (30 mM) in CH3CN/H2O (1:1, pH = 4.75), 12 hours. The
2+
TON was determined by GC‐MS analysis of the crude products.
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S. Zheng, et al.
InorganicChemistryCommunications109(2019)107558
transfer effect of QHQ outside the metal-organic prism cavity allow the
tandem reductions to proceed to efficiently reduce the nitro group using
active H-sources from photo-activated water. The excellent activity and
improved stability suggest that the novel approach for the construction
of supramolecular systems as efficient homogeneous catalysts is pro-
mising and could be extended to other hydrogenation transformations
using light as a clean energy source.
nitroarenes evolution was characterized by GC–MS analysis.
5. Preparation and characterizations
5.1. Synthesis of H4L1
A 250 mL round-bottomed flask equipped with magnetic stir bar
and reflux condenser was charged with 5,5′-methylenediisophthalohy-
drazide (2.00 g, 5.00 mmol) [40], 2-(Diphenylphosphino)benzaldehyde
(6.39 g, 22.00 mmol) and 150 mL ethanol. The mixture was heated at
boiling temperature under magnetic stirring for 12 h. A white pre-
cipitate was formed, which was collected by filtration and dried in
vacuum. Yield: 6.50 g, 87.3%. 1H NMR (400 MHz, DMSO‑d6, ppm) δ
12.11 (s, 4HNH), 8.24 (s, 2Hbenzene), 8.07 (d, J = 4.8 Hz, 4Hbenzene), 7.98
(s, 4Hbenzene), 7.83 (s, 4HCH), 7.55 (t, J = 4.8 Hz, 4Hbenzene), 7.51 (t,
J = 6.0 Hz, 8Hbenzene), 7.34–7.41 (m, 24Hbenzene), 7.19 (d, J = 1.6 Hz,
16Hbenzene), 4.08 (s, 2HCH2). Elemental analysis calcd for
C93H72N8O4P4: H 4.87, C 74.99, N 7.52%. Found: H 4.90, C 74.41, N
7.47%. ESI-MS calcd for C93H72N8O4P4 1489.4659, found 1512.5895
4. Experimental
4.1. Materials and methods
All the chemicals and solvents were of reagent grade quality ob-
tained from commercial sources and used without further purification.
The elemental analyses of C, H and N were performed on a Vario EL III
elemental analyzer. 1H NMR spectra were collected on a Bruker 400 M
spectrometer. ESI mass spectra were obtained from an HPLC-Q-T of
mass spectrometer using acetonitrile as the mobile phase. UV–vis
spectra were collected on an HP 8453 spectrometer. The fluorescence
emission spectra were collected on an Edinburgh FS920. Isothermal
Titration Calorimetry (ITC) were performed on a Nano ITC (TA
Instruments Inc. -Waters LLC). The solution of Ru(bpy)3(PF6)2 was
prepared in CH3CN.
[M + Na]+, 1528.5942 [M + K]+
.
5.2. Preparation of Co–L1
A
solution of Co(NO3)2·6H2O (58.21 mg, 0.20 mmol) and H4L1
Electrochemical measurements were performed with a ZAHNER
ZENNIUM electrochemical workstation with a conventional three-
electrode system with a custom-designed Ag/AgCl electrode as a re-
ference electrode, a platinum silk with 0.5 mm diameter as a counter
electrode, and glassy carbon electrode as a working electrode. Cyclic
voltamograms with the solution concentrations were 0.10 mM for the
cobalt-based compounds and 0.10 M (n-Bu4N)PF6 for the supporting
electrolyte. Electrodes were polished on a MD-Nap polishing pad.
Additions of p-toluene sulfonic acid were made by syringe using a
0.10 M solution in CH3CN. The measurements were performed at room
temperature after the system had been degassed with argon.
(74.48 mg, 0.05 mmol) in CH3OH/CH3CN/C2H5OH (1:1:1, 30 mL) was
stirred for 2 h at room temperature. Then the solution was left for several
weeks at room temperature to give red solid. Yield: 49.61 mg, 53.4%.
Elemental analysis calcd for Co6C279H206N24O12P12·8NO3·5C2H5OH·H2O:
H 4.32, C 62.47, N 8.07%. Found: H 4.52, C 62.78, N 7.80% ESI-MS: m/z:
801.6560 [Co6(L1)3]6+, 974.3839 [Co6(L1)3·NO3
]
and 1233.4789
− 5+
[Co6(L1)3·2NO3
]
.
−
4+
5.3. Synthesis of benzhydrazide
A 250 mL round-bottomed flask equipped with magnetic stir bar
and reflux condenser was charged with 80% hydrazine hydrate
(16 mL), ethyl benzoate (1.50 g, 10.00 mmol) and 100 mL ethanol. The
mixture was heated at boiling temperature under magnetic stirring for
24 h. A white precipitate was formed, which was collected by filtration
and dried in vacuum. Yield: 1.24 g, 91.1%. 1H NMR (400 MHz,
DMSO‑d6, ppm) δ 9.75 (s, 1HNH), 7.82 (d, J = 6.4 Hz, 2Hbenzene), 7.51
(t, J = 5.6 Hz, 1Hbenzene), 7.44 (t, J = 6.0 Hz, 2Hbenzene), 4.48 (s,
2HNH2). Elemental analysis calcd for C7H8N2O: H 5.92, C 61.75, N
20.58%. Found: H 6.17, C 59.83, N 19.67%. ESI-MS calcd for C7H8N2O:
4.2. General procedure for hydrogen production
In a typical experiment, photoinduced hydrogen evolution was
made in a 20 mL flask. Varying amounts of the catalyst, Ru(bpy)32+ and
ascorbic acid in 1:1 CH3CN/H2O were added to obtain a total volume of
5.0 mL. The flask was sealed with a septum, degassed by bubbling argon
for 15 min under atmospheric pressure at room temperature. The pH of
this solution was adjusted to a specific pH by adding H2SO4 or NaOH
and measured with a pH meter. After that, the samples were irradiated
by a 500 W Xenon Lamp, the reaction temperature was 298 K by using a
water filter to absorb heat. The generated photoproduct of H2 was
characterized using a GC 7890 T gas chromatograph equipped with a
5 Å molecular sieve column (0.6 m × 3 mm) and a thermal conductivity
detector; argon was used as the carrier gas. The amount of hydrogen
generated was determined by the external standard method. Hydrogen
in the resulting solution was not measured and the slight effect of the
hydrogen gas generated on the pressure of the flask was neglected for
calculation of the volume of hydrogen gas [39].
136.0637, found 137.0721 [M + H]+, 159.0514 [M + Na]+
.
5.4. Synthesis of HL2
A 250 mL round-bottomed flask equipped with magnetic stir bar
and reflux condenser was charged with benzhydrazide (0.68 g,
5.00 mmol), 2-(diphenylphosphino)benzaldehyde (1.60 g, 5.50 mmol)
and 150 mL ethanol. The mixture was heated at boiling temperature
under magnetic stirring for 12 h. A white precipitate was formed, which
was collected by filtration and dried in vacuum. Yield: 1.83 g, 89.6%.
1H NMR (400 MHz, DMSO‑d6, ppm) δ 12.01 (s, 1HNH), 9.19 (d,
J = 3.6 Hz, 1Hbenzene), 8.09 (s, 1HCH), 7.89 (d, J = 5.6 Hz, 2Hbenzene),
7.58 (d, J = 4.8 Hz, 1Hbenzene), 7.46–7.54 (m, 3Hbenzene), 7.38–7.44 (m,
7Hbenzene), 7.22 (d, J = 3.2 Hz, 4Hbenzene), 6.85 (t, J = 4.8 Hz,
1Hbenzene). Elemental analysis calcd for C26H21N2OP: H 5.18, C 76.46, N
4.3. General procedure for selective hydrogenation of nitroarenes to anilines
In a typical experiment, selective hydrogenation of nitroarenes to
anilines was made in a 20 mL flask. Varying amounts of the p-ni-
2+
troacetophenone, the catalyst, Ru(bpy)3
and ascorbic acid in 1:1
CH3CN/H2O were added to obtain a total volume of 5.0 mL. The flask
was sealed with a septum, degassed by bubbling argon for 15 min under
atmospheric pressure at room temperature. The pH of this solution was
adjusted to a specific pH by adding H2SO4 or NaOH and measured with
a pH meter. After that, the samples were irradiated by a 500 W Xenon
Lamp, the reaction temperature was 298 K by using a water filter to
absorb heat. The generated photoproduct of selective hydrogenation of
6.86%. Found: H 5.29, C 75.39, N 6.75%. ESI-MS calcd for
C
26H21N2OP: 408.1391, found 409.1485 [M + H]+
,
431.1318
[M + Na]+
.
5.5. Preparation of Co–L2
A solution of Co(NO3)2·6H2O (29.10 mg, 0.10 mmol) and HL2
6

S. Zheng, et al.
InorganicChemistryCommunications109(2019)107558
(40.84 mg, 0.10 mmol) in CH3OH/CHCl3 (1:1, 10 mL) was stirred for
2 h at room temperature. Then the solution was left for several days at
room temperature to give orange solid. The solid were dried in vacuum.
Yield: 28.14 mg, 56.1%. Elemental analysis calcd for Co
(C26H20N2OP)2·NO3·CH3OH·2H2O: H 4.82, C 63.41, N 6.98%. Found: H
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